Declassified MI5 file shows Nazi spy almost changed course of war

A Nazi spy came within days of uncovering one of the Allies' most important missions and possibly changing the direction of the Second World War.

The story of a Portuguese wireless operator and the dramatic decision to pluck him from his vessel on the high seas to prevent him from betraying the position of a huge convoy bound for North Africa is revealed for the first time in a declassified MI5 file released by the National Archives.

Gastao de Freitas Ferraz was being paid by German intelligence to send coded messages about convoys to U-boat commanders and was on the tail of the Allied warships.